Polymeric water soluble thickening agents are widely used for many purposes and many such agents of different chemical types are commercially available. The diversity of available products is an indicator that they are not all equally useful. It is not unusual to find some thickening agents which perform well in a certain environment and not at all in another environment. In fact, in some uses no one thickening agent is completely satisfactory and there is a continual need and a continuing search for new thickening agents to satisfy many of the unmet needs. Latex paint thickening is a good example, where the market is actively seeking an agent which will provide stable thickening as well as other properties such as flow and leveling.
U.S. Pat. Nos. 2,921,930 and 3,301,829 propose to make thickening agents by esterification of anhydride containing polymers. While certain of these polymeric esters provide thickening power, the viscosity of the aqueous system is not stable to storage. U.S. Pat. No. 3,499,876 proposes to make water soluble thickening agents from certain monomers. While no information is available therein to judge storage stability, a principal problem is the limited range of monomers which can be copolymerized together.
It is an object of this invention to provide aqueous storage stable thickening agents which may be prepared from a variety of monomers.